Depending on the circumstances it can be desirable and/or particularly important to be able to sense the presence of various gases which might be dangerous or explosive. These include carbon monoxide, carbon dioxide, propane, methane, as well as other potentially explosive gases.
A variety of sensors are known which can detect various gases. These sensors are based on different technologies and have different performance characteristics and different cost characteristics. One technology of ongoing interest is represented by electrochemical sensors. This class of sensors is potentially reliable and inexpensive.
Electrochemical sensors can be designed so as to be responsive to a gas of interest and to be highly sensitive. They respond to a gas of interest with a respective output current.
Advantages of electro-chemical sensors are that they are very robust and difficult to poison. Acid used in such sensors is such that the sensors can operate over a wide pH range. Another aspect of robustness of electro-chemical sensors relates to the amount of platinum used on the electrodes. The platinum can “wear” over time. This results in a change in sensitivity as a result of changing the surface and activity points in the sensor.
It is recognized that exposures to gases that cause a response in the sensor cause a slight decline in sensor sensitivity.
FIG. 1 illustrates sensitivity variations of a typical electro-chemical sensor over time, for example, a period of years, with and without gas exposure. As is apparent from FIG. 1, where an electro-chemical sensor has been exposed to relatively high concentrations of gases, the sensitivity experiences a greater decline than is the case where the respective sensor has not been exposed to high concentrations of gas.
To realize the various benefits of using electro-chemical sensors, it would be desirable to be able to adjust the sensitivity over the lifetime operation of the respective sensor so as to maintain more consistent long-term performance of the respective sensors than would otherwise be possible. Preferably, such sensitivity monitoring and adjustments could be implemented in a variety of circuit configurations which incorporate electro-chemical sensors.